1. Field of the Invention
This invention relates to a gas supplying apparatus for supplying high pressure gas flowing from gas containers to chemical processing apparatus by reducing said gas pressure.
Moreover, this invention relates to a vapor-phase growth plant comprising a dopant gas conduction means for supplying high pressure dopant gas flowing from dopant gas containers to vapor-phase growth apparatus by reducing said dopant gas pressure.
2. Description of the Prior Art
A well known prior art gas supplying apparatus is configured such that chemical processing gas, filled as compressed gas or liquefied gas in a gas container or gas cylinder, is supplied through piping system via pressure reducing valve to chemical processing apparatus.
FIG. 4 illustrates the schematic configuration of a vapor-phase growth plant as an example of such conventional gas supplying apparatus.
According to the drawings, the vapor-phase growth plant has a gas supplying container(or gas cylinder) 61 which is filled up with dopant gas (for example, H.sub.2 diluted B.sub.2 H.sub.6 : diborane gas) 62. The dopant gas flows through a dopant gas supply piping 64 via a pressure reducing valve 63 to a thin film growth chamber 65a disposed in a vapor-phase growth apparatus 65. In the thin film growth chamber 65a, the dopant gas is supplied on a substrate which is loaded in the chamber for growing thin film by vapor-phase growth on the surface of the substrate.
For the purpose of removing any contaminants in the dopant gas supply piping 64 which may intrude from surroundings, a gas purging apparatus is connected to the dopant gas supply piping 64. The gas purging apparatus is equipped a purging gas supplying conduit 66 and a purging gas discharge conduit 67 respectively therewith.
As for purging gas, nitrogen gas (N.sub.2) or rare gas (Ar, He etc.) are adopted. The part which is closed by a dotted line in the FIG. 4 shows cylinder cabinet 68 for storing the gas supplying container 61.
As shown above, in the prior art, the cylinder cabinet 68 is disposed on one-for-one correspondence to the vapor-phase growth apparatus 65. The reason for this is that a gas supplying container commonly used, as usual, has some variance in dopant gas concentration. Therefore, upon replacing of the dopant gas supplying container, dopant gas concentration may vary for some extent, which may result in variance on atomic concentration of the grown thin film produced in the vapor-phase growth apparatus 65, though operated in the same situation or the same film growing condition.
In consequence, to avoid undesirable variance of dopant concentration in the grown thin film caused by replacing the dopant gas supplying container, thin film growth condition by the vapor-phase growth apparatus must be adjusted respectively in accordance with the dopant gas concentration of each dopant gas supplying container.
However, since the cylinder cabinet 68 is disposed on one-for-one correspondence to the vapor-phase growth apparatus 65 in the conventional vapor-phase growth plant, the following problem arise:
(1) As the number of vapor-phase growth apparatus 65 increases, the number of cylinder cabinet 68 must be increased, which results in the increase of plant installation cost. PA0 (2) In order to avoid variance in grown thin film quality (dopant concentration) upon replacing of gas supplying containers, the production condition must be adjusted, which result in the lesser productivity because of the increase of adjusting time. PA0 (3) Upon replacing of gas supplying containers, such troublesome operations as the substituting of residual gas in the dopant gas supplying pipe with the purging gas would be required. PA0 (4) Ever since the gas supplying container is rather small in volume, duration on continuous operation is short.